Routers are used in telecommunication networks as an interface, for example, between a backbone network based on an Internet protocol and an access network, for example a DSL network; DSL=Digital Subscriber Line. DSL networks are constructed as ADSL, SDSL, VHDSL, for example, where A stands for Asymmetric, S for Symmetric and VH for Very High.
A router usually contains a packet memory and a readout unit and is used to route and receive information packets. The received information packets are temporarily stored in the packet memory. Routers which do not distinguish between service qualities operate on the FIFO (first in first out) principle, that is to say each packet is forwarded immediately on receipt. Routers which distinguish between different service qualities and have to handle each individual data flow separately, evaluate parts of each packet and compares it with a list of classifications which enable the assignment of the packet to a data flow. After the assignment, only pointers to the information packets are temporarily stored in a buffer memory. The classifier is provided in order to extract the pointers of the information packets from the received data flow, to evaluate them and to feed them to at least one buffer memory. The readout unit is used to read out the temporarily stored pointers and, by means of the read-out pointers, to detect and read out the information packets assigned to the read-out pointers. A so-called weighted round robin (WRR) mechanism is used for the readout procedure. In this case, different buffer memory areas are read out one after the other and in predetermined time windows. This process ensures that, at the outputs of the router, each data flow and each service class receives the bandwidth provided for it. The sequence of the packets between the various data flows can certainly change, but the packet sequence does not change within a data flow.
Information packets are usually transmitted in different, so-called Quality of Service (QoS) classes. A quality of service class specifies the so-called Voice over Internet Protocol (VoIP), for example. Another quality of service class specifies the so-called Best Effort (BE) service, for example. Voice, data, video, Internet web pages, etc., can be transmitted as information in information packets.
The routers which support a service-specific charging system, have to classify and route each information packet individually while taking different requirements into account.
The overall bandwidth of a transmission channel is distributed among the types of services on offer, and is comparable to the division of a circle into sectors. “Weighted” signifies that the sectors can be of unequal size to meet the specified traffic profile. The trick for QoS is that the sectors for VoIP are always slightly larger than the requirement, and that they follow one another sufficiently quickly. For best effort traffic, there is no quality guarantee and the provided bandwidth can be less than that requested. The sectors in the WRR may be too small in comparison with the emerging traffic. Best effort packets can therefore collide, be delayed or disappear altogether.
The search for pointers requires time, thereby impairing the processing speed of the router. In addition, a longer search can lead to gaps occurring in the output information packet stream, in which no information packets are transmitted, which leads to a lower information rate. Furthermore, a predetermined time slot is reserved for the readout of a stacking area, so that the processing of the stacking area is impaired by a longer search, which can cause an overflow of the stacking area, leading to information loss.
In addition, a process is implemented, which removes under random control the individual information packets that were temporarily stored but not yet read out, if the data transfer rate of the received information packets exceeds the data transfer rate of the read-out information packets. This process is termed RED=Random Early Discard, or also RIO=RED with In and Out. Received information packets can also be removed instead of the temporarily stored ones. The removed information packets are not transmitted to the destination address and are irretrievably lost. The process is used for so-called load balancing, that is to say a controlled throughput in relation to traffic volume, in order to prevent blocking, in particular. In order to facilitate RED, a knowledge of the occupancy levels of the stacking areas is necessary. The occupancy levels of the stacking areas are monitored by means of one or more separate detection units. Scanning, in particular, of the stacking areas at short time intervals is necessary to achieve this. The detected occupancy levels are transmitted to the RED processing units, which arrange removal of information packets if an occupancy level exceeds a predetermined threshold value.